I'm guessing they don't want to maintain and build and test x86_64 versions of all the macos libraries like Appkit and UIKit (including large changes like liquid glass) when they are no longer shipping x86_64 macOS versions. Which is not entirely unreasonable as I'm sure it takes a lot of effort to keep the whole ui library stack working properly on multiple archs.
Perhaps that's what they're hinting about with the note about a "subset of Rosetta". So maybe there is hope that the core x86_64 binary translator will stick around for things like VM and emulation of generic (linux? wine?) binaries, but they don't want to maintain a whole x86_64 macOS userspace going forward.
Space savings from not shipping fat binaries for everything will probably also be not insignificant. Or make room for a new fat binary for a future "arm64v2" :)
Perhaps that's what they're hinting about with the note about a "subset of Rosetta". So maybe there is hope that the core x86_64 binary translator will stick around for things like VM and emulation of generic (linux? wine?) binaries, but they don't want to maintain a whole x86_64 macOS userspace going forward.
Space savings from not shipping fat binaries for everything will probably also be not insignificant. Or make room for a new fat binary for a future "arm64v2" :)